The present invention refers to a method for non-continuous rolling of multiple billets fed from a billet-heating furnace set upstream of a roll train. The invention also refers to a plant which is particularly suitable for the implementation of said method.
As is known to the persons skilled in the branch, there are two methods generally adopted for rolling the billets coming out of a billet-heating furnace which is set upstream of a roll train, aligned with the latter. The first method is discontinuous, whilst the second method is continuous.
In discontinuous methods, the billets are fed, one at a time, into the roll train, at time intervals which, for reasons of productivity, must be as short as possible, for example around 5 seconds.
Discontinuous rolling methods have by now experienced a consolidated use over time and have a plant cost lower than that of continuous methods. They present, however, a number of drawbacks. First of all, for each billet, evidently a feeding-in is required between the cylinders of each roll stand making up the roll train. There thus exists a high risk of jamming, with consequent stoppage of the plant and waste of material. A high degree of wear of the rolls and of the devices for feeding the billets in between them is moreover to be expected, given the high number of feed-ins. In addition, for each billet, a head-cropping operation is required, with consequent wear on the blades of the billet shear and waste of material.
Continuous methods, instead, envisage rolling of a continuous billet which is obtained by welding the head of one billet coming out of the heating furnace to the tail of the billet that came out before it and is already introduced into the first stand of the roll train, and so forth.
Continuous rolling methods require more costly plants than discontinuous methods and are particularly justified for high levels of output.
Continuous rolling methods are, for instance, described, in the patents EP-0761330 and EP-0832700, to which the reader is referred if further clarifications were necessary.
The general purpose of the present invention is to overcome the drawbacks of the prior art by providing a method for rolling billets coming out of a heating furnace, which, albeit having contained plant costs, i.e., lower than those involved in a continuous method, enables an output greater than that of discontinuous methods.
Another purpose of the invention is to make available a rolling method that is easy to implement also by modifying already existing plants.
A further purpose of the invention is to provide a method that enables rolling also of short billets, for example ones having a length of 4.6 m, which are difficult to use in continuous methods, in that their rolling time may be shorter than the time of the welding cycle.
The above purposes are achieved by a method and plant having the characteristics specified in the attached claims.